MOSCOW, June 10 (Reuters) - President Vladimir Putin denied on Tuesday waging war on Internet freedoms, saying restrictions imposed by Russia were meant mainly to protect children from indecent content.

Trying to calm fears he is clamping down on Internet freedoms to head off criticism and protests, Putin told a forum on Internet start-up companies: "We've debated these restrictions on paedophilia, on the promotion of drugs, terrorism or advocating suicide a lot."

"But listen, we are all grown ups, let's stop. Let's leave our children in peace," he said. "But there is another matter, that under this pretext ... one should not introduce any restrictions on civil liberties and the free market."

Russia has passed legislation banning sites that contain child pornography, drug-related or extremist material, or advocate suicide to protect children, but some critics say the law opened the door to restrictions over more general content.

The government has also moved against blogs, one of the few popular media platforms still outside the Kremlin's reach. Putin signed a law last month requiring websites that attract more than 3,000 daily visits to register by name with a communications watchdog.

With 61 million users, Russia is Europe's fastest-growing Internet audience, according to a 2013 report by industry body comScore, and e-commerce is seen as a growth sector in Russia's economy weakened by Western sanctions over Ukraine.

But social media and the Internet are used by Putin's opponents to criticise him and have been used to organise rallies against him, including when he faced mass protests in cities such as Moscow in the winter of 2011-12.

The Kremlin denies allegations of censorship or pressure on the media and Internet users, and says Russians have the right to express their opinions and stage protests.

Putin, who has described the Internet as a CIA project, said some kind of regulation was unavoidable.

"This is a huge segment of the market and it is impossible not to regulate ... every day a third of our population uses the Internet and of course, there has to be some regulation," he told delegates.

But he added: "Internet communication in our country has turned into a very lucrative business. Let me remind you that this is 8.5 percent of GDP. And the size of the market involved in the online business is worth more than 5 trillion roubles. This is a great business." (reporting by Maria Kiselyova, writing by Elizabeth Piper, editing by Timothy Heritage)